Generally, a motor that outputs rotational movement is used as an actuator for a pump device or compressor device in which a piston moves rectilinearly within a cylinder. Therefore, problems are encountered in that power is not transmitted efficiently because the rotational movement must be converted to rectilinear movement by a crankshaft or the like between an output shaft of the motor and the piston.
In view of this, the configuration described in connection with the electromechanical converter disclosed in JP-B 6-91727 has been considered for use as a linear actuator. As shown in FIGS. 7(A) and (B), the linear actuator disclosed herein includes two or four inner yokes 103, 203, two or four outer yokes 104, 204 disposed so as to form gaps 109, 209 with outer surfaces of the inner yokes 103, 203, coils (not shown) wound around the outer yokes 104, 204, and magnets 106, 206 disposed in the gaps 109, 209. A layered structure is used for the inner yokes 103, 203 and the outer yokes 104, 204 so that multiple magnetic thin plates are layered on opposite sides so as to describe an arc, and arcuate components are used as magnets 106, 206 to match the shape thereof.
Another possibility is shown in FIG. 7(C), wherein a cylindrical inner yoke 303 and a cylindrical outer yoke 304 face each other via a prescribed gap 309, and a cylindrical magnet 306 is disposed in the gap 309.
All these structures appear as shown in FIG. 7(D) when cut in an axial direction. When an alternating current flows through a coil 108, the orientation alternates between a magnetic field created between the inner yokes 103, 203, 303, the outer yokes 104, 204, 304, and one of the leg portions, and a magnetic field created between the inner yokes 103, 203, 303, the outer yokes 104, 204, 304, and the other leg portion. Therefore, the magnets 106, 206, 306 oscillate in the axial direction, so a movable member (not shown) formed integrally with the magnets also oscillates in the axial direction, and reciprocating rectilinear movement can be outputted from the movable member.
However, with the configuration shown in FIGS. 7(A) and (B), in order for the gaps 109, 209 to have an arcuate shape, the magnetic thin plates must be layered while being shifted in small increments by using a special layered structure when manufacturing the inner yokes 103, 203 and the outer yokes 104, 204, which makes mass production difficult. Also, precise polishing is necessary when manufacturing curved magnets 106, 206, which also makes mass production difficult. Similarly, it has been difficult to manufacture the ring-shaped inner yoke 303, outer yoke 304, and magnet 306 shown in FIG. 7(C). Furthermore, problems have been encountered when disposing a plurality of magnets in relation to a movable member in that assembly operations require much labor because the magnets attract or repel each other.